This invention relates to a process for the preparation of catalysts of the double metal cyanide complex class.
The preparation of double metal cyanide complex catalysts, e.g., a metal hexacyanometallate catalyst which is useful for alkylene oxide polymerization, from a metal salt and an alkali metal hexacyanometallate requires the removal of the alkali metal halide formed during the reaction. Due to the small particle size of the metal hexacyanometallate, filtration is not practical. Centrifugation, dialysis, or conversion to a filterable metal hydroxide salt are the methods which have been described previously in the literature. Various methods have been outlined in U.S. Pat. Nos. 3,427,256; 3,941,849; 4,472,560; and 4,477,589. The teachings of these patents are incorporated herein by reference. These prior art methods require sophisticated equipment to achieve separation. The present invention provides a method which facilitates the use of filtration to prepare double metal cyanide complex catalysts.